Control circuit for outputting pulse width modulation control signal with zero-crossing detection

ABSTRACT

The present disclosure provides a control circuit and a control method, where the control circuit includes: a signal detection unit, a ZCD signal acquisition unit, a signal selection unit, a frequency limiting unit, and a PWM control signal generation unit; where the signal detection unit, the ZCD signal acquisition unit, the signal selection unit, the frequency limiting unit, and the PWM control signal generation unit are connected in cascade. The control circuit and the control method provided in the present disclosure reduce processing delay of a ZCD signal and improve signal processing accuracy of a PFC system.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to Chinese Patent Application No.201810476335.9, filed on May 17, 2018 and entitled “CONTROL CIRCUIT ANDCONTROL METHOD”, which is hereby incorporated by reference in itsentirety.

TECHNICAL FIELD

The present disclosure relates to the field of circuits and, inparticular, to a control circuit and a control method.

BACKGROUND

With the rapid development of electronic technologies, the power ratingof power supply equipment continuously increases, and the standard ofharmonic currents gets universal and lowered. Nowadays, power factorcorrection (PFC) converters are increasingly used in power supplydesigns to improve power factors of electric equipment. The conventionalbridge PFC converter is widely used in the front end of AC/DC powerstage due to its simple circuit structure and low common-mode noise.However, the energy transfer path will cause high conduction andswitching loss as more semiconductor devices are used due to thepresence of a rectifying bridge.

In order to reduce the loss of switches in the PFC circuit, a bridgelessPFC has been applied. For application of the bridgeless PFC, thecritical problems include phase detection of alternating voltage andzero current detection when the PFC inductor current is in a criticaldiscontinuous mode (DCMB for short).

In prior art, an AC voltage of the input PFC circuit is obtained bydetecting the inductor voltage at the input of the PFC circuit, and azero-crossing detection signal of this voltage is extracted and sent toa DSP/MCU, which processes the signal in a digital way throughsequentially-executed operations such as determination of the phase ofthe input voltage, selection of the zero-crossing detection (ZCD forshort) signal, frequency limiting operation on the zero-crossingdetection signal, and the like to generate the control signals of theswitches in the PFC circuit.

In the prior art, the operations such as processing of the ZCD signal bythe DSP/MCU and frequency limiting operation require high performance ofthe DSP/MCU, especially when used in high-frequency applications since asignificant signal delay will be introduced by DSP/MCU while processinghigh-frequency ZCD signals, if worse, the accuracy of signal processingin the entire system where the PFC is located will be affected.

SUMMARY

The present disclosure provides a control circuit and a control method,which reduce processing delay of a ZCD signal and improve signalprocessing accuracy of a PFC system.

The present disclosure provides a control circuit, including:

a signal detection unit, coupled to an AC-side inductor of an AC/DCconverter, which is configured to detect a voltage of the AC-sideinductor and output an inductor voltage detection signal, wherein theinductor voltage detection signal is an AC signal;

a ZCD signal acquisition unit, coupled to the signal detection unit,which is configured to receive the inductor voltage detection signal,and generate a zero-crossing detection signal of the voltage of theAC-side inductor;

a signal selection unit, coupled to the ZCD signal acquisition unit,which is configured to receive the zero-crossing detection signal, andgenerate an inductor voltage frequency indication signal according tothe zero-crossing detection signal;

a frequency limiting unit, coupled to the signal selection unit, whichis configured to receive the inductor voltage frequency indicationsignal and a pulse signal of a preset threshold frequency, and generatea ZCD trigger signal of which with the frequency is no greater than thepreset threshold frequency; and

a PWM control signal generation unit, coupled to the frequency limitingunit, which is configured to receive the ZCD trigger signal and generatea PWM control signal for the AC/DC converter according to the ZCDtrigger signal.

The present disclosure further provides a control method for operatingthe control circuit described above, comprising:

detecting the voltage of the alternating current (AC)-side inductor;

generating the zero-crossing detection signal for the voltage of theAC-side inductor according to the voltage of the AC-side inductor;

generating the inductor voltage frequency indication signal according tothe zero-crossing detection signal;

generating the ZCD trigger signal of a frequency no greater than thepreset threshold frequency, according to the inductor voltage frequencyindication signal and the pulse signal of a preset threshold frequency;and

generating the PWM control signal for the AC/DC converter according tothe ZCD trigger signal.

The present disclosure provides a control circuit and a control method,where the control circuit includes: a signal detection unit, a ZCDsignal acquisition unit, a signal selection unit, a frequency limitingunit, and a PWM control signal generation unit; where the signaldetection unit, the ZCD signal acquisition unit, the signal selectionunit, the frequency limiting unit, and the PWM control signal generationunit are connected in cascade; the signal detection unit is furtherconnected to an AC-side inductor of an AC/DC converter and configured todetect a voltage of the AC-side inductor and generate an inductorvoltage detection signal, where the inductor voltage detection signal isan AC signal; the ZCD signal acquisition unit receives the inductorvoltage detection signal, generates a zero-crossing detection signal forthe voltage of the AC-side inductor, and sends the zero-crossingdetection signal to the signal selection unit; the signal selection unitreceives the zero-crossing detection signal, generates an inductorvoltage frequency indication signal according to the zero-crossingdetection signal, and sends the inductor voltage frequency indicationsignal to the frequency limiting unit; the frequency limiting unitreceives the inductor voltage frequency indication signal, generates,according to a pulse signal of a preset threshold frequency, a ZCDtrigger signal of a frequency no greater than the preset thresholdfrequency; and the PWM control signal generation unit receives the ZCDtrigger signal such that the PWM control signal generation unitgenerates a PWM control signal for the AC/DC converter according to theZCD trigger signal. The control circuit and the control method providedin the present disclosure reduce processing delay of a zero-crossingdetection signal and improve signal processing accuracy of a PFC system.

BRIEF DESCRIPTION OF DRAWINGS

In order to describe technical solutions in embodiments of the presentdisclosure or in the prior art more clearly, accompanying drawings usedin the description of the embodiments or the prior art will be brieflydescribed hereunder. Obviously, the described drawings are merely someembodiments of present disclosure. For persons skilled in the art, otherdrawings may be obtained based on these drawings without any creativeeffort.

FIG. 1A is a schematic structural diagram of a circuit according to afirst conventional PFC system;

FIG. 1B is a schematic structural diagram of a circuit according to asecond conventional PFC system;

FIG. 1C is a schematic structural diagram of a circuit according to athird conventional PFC system;

FIG. 2 is a schematic structural diagram of a bridgeless PFC controlcircuit;

FIG. 3 is a schematic structural diagram of a control circuit accordingto a first embodiment of the present disclosure;

FIG. 4 is a schematic structural diagram of a control circuit accordingto a second embodiment of the present disclosure;

FIG. 5 is a schematic structural diagram of a frequency limiting unitaccording to a first embodiment of the present disclosure;

FIG. 6 is a schematic diagram illustrating timing of signals of afrequency limiting unit according to a first embodiment of the presentdisclosure;

FIG. 7 is a schematic structural diagram of a frequency limiting unitaccording to a second embodiment of the present disclosure;

FIG. 8 is a schematic diagram illustrating timing of signals of afrequency limiting unit according to a second embodiment of the presentdisclosure;

FIG. 9 is a schematic diagram illustrating timing of signals of afrequency limiting unit according to the present disclosure;

FIG. 10 is a schematic diagram of a relationship between angle andoperating frequency during a half sine cycle of mains frequencyaccording to the present disclosure;

FIG. 11 is a schematic structural diagram of a control circuit accordingto a third embodiment of the present disclosure;

FIG. 12A and FIG. 12B show a schematic diagram illustrating timing of aninductor voltage detection signal and a zero-crossing detection signalof a control circuit according to a third embodiment of the presentdisclosure;

FIG. 13A and FIG. 13B show a schematic diagram illustrating timing of aninductor voltage frequency indication signal of a control circuitaccording to a third embodiment of the present disclosure;

FIG. 14A and FIG. 14B show a schematic diagram illustrating timing of aZCD trigger signal of a control circuit according to a third embodimentof the present disclosure;

FIG. 15 is a schematic structural diagram of a signal detection unitaccording to a first embodiment of the present disclosure;

FIG. 16 is a schematic structural diagram of a signal detection unitaccording to a second embodiment of the present disclosure;

FIG. 17 is a schematic structural diagram of a signal detection unitaccording to a third embodiment of the present disclosure;

FIG. 18 is a schematic structural diagram of a ZCD signal acquisitionunit according to a first embodiment of the present disclosure;

FIG. 19 is a schematic structural diagram of a ZCD signal acquisitionunit according to a second embodiment of the present disclosure;

FIG. 20 is a schematic structural diagram of a ZCD signal acquisitionunit according to a third embodiment of the present disclosure;

FIG. 21 is a schematic structural diagram of a ZCD signal acquisitionunit according to a fourth embodiment of the present disclosure;

FIG. 22 is a schematic structural diagram of a signal selection unitaccording to a first embodiment of the present disclosure;

FIG. 23 is a schematic structural diagram of a signal selection unitaccording to a second embodiment of the present disclosure;

FIG. 24 is a schematic structural diagram of a signal selection unitaccording to a third embodiment of the present disclosure;

FIG. 25 is a schematic structural diagram of a signal selection unitaccording to a fourth embodiment of the present disclosure;

FIG. 26A and FIG. 26B show a schematic diagram illustrating a principleof acquisition of a phase signal by a signal selection unit according toa first embodiment of the present disclosure;

FIG. 27A and FIG. 27B show a schematic diagram illustrating a principleof acquisition of a phase signal by a signal selection unit according toa second embodiment of the present disclosure; and

FIG. 28 is a schematic flow chart of a control method according to afirst embodiment of the present disclosure.

DESCRIPTION OF EMBODIMENTS

The technical solutions in the embodiments of the present disclosurewill be described hereunder clearly and completely with reference toaccompanying drawings in the embodiments of the present disclosure.Obviously, the described embodiments are only a part of embodiments ofthe present disclosure, rather than all embodiments of the presentdisclosure. All other embodiments obtained by persons of ordinary skillin the art based on the embodiments of the present disclosure withoutany creative effort shall fall into the protection scope of the presentdisclosure.

Terms such as “first”, “second”, “third”, “fourth”, etc. (if present) inthe specification and the claims as well as the described accompanydrawings of the present disclosure are used to distinguish similarobjects, but not intended to describe a specific order or sequence. Itwill be appreciated that the data used in this way may beinterchangeable under appropriate circumstances, such that theembodiments of the present disclosure described herein can beimplemented in an order other than those illustrated or describedherein, for instance. Moreover, terms such as “include” and “have” andany variation thereof are intended to cover a non-exclusive inclusion,e.g., processes, methods, systems, products or devices that encompass aseries of steps or units are not necessarily limited to those steps orunits that are clearly listed, but may include other steps or units thatare not clearly listed or inherent to these processes, methods, productsor devices.

FIG. 1A-FIG. 1C are schematic structural diagrams of a circuit of aconventional PFC system. The conventional Boost PFC converter as shownin FIG. 1A is widely used in a front end of the AC/DC power stage due toits simple circuit structure and low common-mode noise. However, due tothe existence of a rectifying bridge in the conventional PFC converter,energy passes through three semiconductor devices to form a transferpath, resulting in high conduction and switch loss. is subjected to

In order to meet needs for power supply products with high efficiencyand high power density, and to improve the performance of the Boost PFCconverter, the bridgeless PFC has been developed. Since there is norectifying bridge, the number of semiconductor devices for energytransfer is reduced, and the efficiency is improved. FIG. 1B shows abi-directional switch bridgeless PFC; and FIG. 1C shows a totem-polebridgeless PFC. In these two bridgeless PFCs the unrectified Vac isapplied on the inductors L1, and the energy stored in the inductorchanges with polarity of the input Vac, furthermore, more switch powerdevices need to be controlled, which requires more complex voltagedetection of the inductor current and control method than theconventional Boost PFC.

Specifically, FIG. 2 is a schematic structural diagram of a bridgelessPFC control circuit applied to control the circuits of FIG. 1B and FIG.1C. A voltage signal of the PFC inductor L is detected via an auxiliarywinding Laux, and a positive ZCD signal and a negative ZCD signal of Vacof the L are acquired through signal processing and sent to the ICController. The IC Controller may be a digital processor such as aDSP/MCU. The IC controller determines a phase of the voltage of theinductor L, selects the positive or negative ZCD signal according to thephase, and performs frequency limiting on the selected ZCD signal.Finally, a PWM control signal is generated to control switches Q1 andQ2.

However, using a processor of the IC Controller to execute the selectionand the frequency limiting of the inductor voltage ZCD signal as well asthe generation of the PWM control signal will cause a considerable delayto the signal. Especially when applied in the high-frequency field, thedelay on control signals of the switches will have an adverse effect oncontrol rapidity and accuracy of the entire system.

Therefore, in order to solve the problem in the prior art describedabove, the present disclosure provides a control circuit, according towhich some of the functions implemented by the processor in the priorart are realized by means of analog circuits, thereby reducing the delayin processing ZCD signal, and improving the accuracy of signalprocessing in the PFC system. The technical solutions of the presentdisclosure will be described hereunder in detail with specificembodiments. The following specific embodiments may be combined witheach other, and the same or similar concepts or processes may not berepeated in some embodiments.

Specifically, FIG. 3 is a schematic structural diagram of a controlcircuit according to a first embodiment of the present disclosure. Inthe first embodiment as shown in FIG. 3, the control circuit includes: asignal detection unit 1, a ZCD signal acquisition unit 2, a signalselection unit 3, a frequency limiting unit 4, and a PWM control signalgeneration unit 5.

The signal detection unit 1, the ZCD signal acquisition unit 2, thesignal selection unit 3, the frequency limiting unit 4, and the PWMcontrol signal generation unit 5 are connected in cascade.

The signal detection unit 1 is further connected to an AC-side inductorof an AC/DC converter and configured to detect a voltage of the AC-sideinductor and output an inductor voltage detection signal, where theinductor voltage detection signal is an AC signal. Optionally, theinductor in this embodiment is an input inductor of a bridgeless PFC.

The ZCD signal acquisition unit 2 receives the inductor voltagedetection signal of the signal detection unit 1, generates azero-crossing detection signal of the inductor voltage, and sends thezero-crossing detection signal to the signal selection unit 3.

The signal selection unit 3 receives the zero-crossing detection signal,generates an inductor voltage frequency indication signal according tothe zero-crossing detection signal, and sends the inductor voltagefrequency indication signal to the frequency limiting unit 4.

The frequency limiting unit 4 receives the inductor voltage frequencyindication signal transmitted by the signal selection unit 3, andgenerates, according to a pulse signal of a preset threshold frequency,a ZCD trigger signal with a frequency no greater than the presetthreshold frequency, and transmits the ZDC trigger signal to the PWMcontrol signal generation unit 5.

The PWM control signal generation unit 5 receives the ZCD trigger signaltransmitted by the frequency limiting unit 4, and generates a PWMcontrol signal for the AC/DC converter according to the ZCD triggersignal. Optionally, the PWM control signal generation unit 5 in thisembodiment may be a digital processor.

Optionally, the signal detection unit 1, the ZCD signal acquisition unit2, the signal selection unit 3 and the frequency limiting unit 4 in thisembodiment are constructed with analog circuits.

In summary, the control circuit provided in this embodiment combines thedetection of the inductor voltage, the acquisition and the selection ofthe ZCD signal, and the frequency limiting of the ZCD signal together bymeans of different units, which, subsequent to logical processing,generates only a single ZCD trigger signal, so that the PWM controlsignal generation unit generates a PWM control signal according to theZCD trigger signal. Compared with the prior art where the selection andthe frequency limiting of the inductor voltage ZCD signal as well as thegeneration of the PWM control signal are all implemented by a digitalprocessor, the signal processing procedure is simplified, the delay ofcontrol signal is eliminated, the requirement on performance of theprocessor is reduced, therefore the requirement of controlling of theentire PFC system is met due to improved accuracy of the signalprocessing in the PFC system.

Further, FIG. 4 is a schematic structural diagram of a control circuitaccording to a second embodiment of the present disclosure. The controlcircuit in the second embodiment as shown in FIG. 4 is based on theembodiment as shown in FIG. 3, where the frequency limiting unit isconfigured such that: a first edge signal of the ZCD trigger signal isgenerated when both of the pulse signal of the preset thresholdfrequency and the inductor voltage frequency indication signal are athigh voltage levels; the ZCD trigger signal is not inverted when thepulse signal at the preset threshold frequency is at high voltage level;when a descending edge of the pulse signal of the preset thresholdfrequency arrives, if the inductor voltage frequency indication signalis at low voltage level, then the ZCD trigger signal is inverted tooutput a second edge signal for the ZCD trigger signal, if the inductorvoltage frequency indication signal is at high voltage level, then theZCD trigger signal is inverted to output a second edge signal when anext descending edge of the inductor voltage frequency indication signalarrives.

One possible implementation of the above-described embodiment lies in:the first edge signal is at high voltage level and the second edgesignal is at low voltage level.

Specifically, FIG. 5 is a schematic structural diagram of a frequencylimiting unit according to a first embodiment of the present disclosure.As shown in FIG. 5, a frequency limiting unit in this embodimentincludes a first logical OR gate operator. One input of the firstlogical OR gate receives the pulse signal f max of the preset thresholdfrequency, transmitted by a PWM control signal generation unit (i.e. theIC Controller in the drawing), the other input receives the inductorvoltage frequency indication signal V_(ZCD), sent from the signalselection unit; the first logical OR gate operator performs an ORoperation for f max and V_(ZCD), and the first logical OR gate operatorgenerates a ZCD trigger signal flimit.

Specifically, FIG. 6 is a schematic diagram illustrating timing ofsignals of a frequency limiting unit according to a first embodiment ofthe present disclosure. f max is the pulse signal of the presetthreshold frequency transmitted by the PWM control signal generationunit. V_(ZCD) is the inductor voltage frequency indication signal, andthe ZCD trigger signal flimit is generated after V_(ZCD) and f max aresubjected to a logical OR operation. Optionally, a pulse width of thePWM is calculated via loop control, depending on an input voltage and anoutput load. At the time t₂, both of the pulse signal f max of thepreset threshold frequency and the inductor voltage frequency indicationsignal V_(ZCD) are at high voltage levels, a first edge signal for theZCD trigger signal flimit is generated; during a period when the pulsesignal f max of the preset threshold frequency is at high voltage level,the ZCD trigger signal flimit is not inverted, maintaining the highvoltage level; during the time period [t₃-t₄], the ascending edge ofV_(ZCD) is invalid, the ZCD trigger signal flimit is not inverted,maintaining the high voltage level; at the time t₄, a descending edge ofthe pulse signal f max of the preset threshold frequency arrives, atthis time the inductor voltage frequency indication signal V_(ZCD) is atlow voltage level, and the ZCD trigger signal flimit is inverted tooutput a second edge signal. During the time period [t₆-t₇], theascending edge of V_(ZCD) is invalid, the ZCD trigger signal flimit isnot inverted, maintaining the high voltage level. If the inductorvoltage frequency indication signal V_(ZCD) is at high voltage level,taking the time t₇ as an example, then the ZCD trigger signal flimitmaintains high voltage level until a next descending edge of theinductor voltage frequency indication signal V_(ZCD) arrives, that is,at the time t₈, the ZCD trigger signal flimit is inverted to output asecond edge signal. In an implementation of this embodiment, the firstedge signal is at high voltage level, and the second edge signal is atlow voltage level.

Another possible implementation lies in: the first edge signal is at lowvoltage level and the second edge signal is at high voltage level.Specifically, FIG. 7 is a schematic structural diagram of a frequencylimiting unit according to a second embodiment of the presentdisclosure. As shown in FIG. 7, a frequency limiting unit in thisembodiment includes a logical NOR gate operator. One input of the firstlogical NOR gate receives the pulse signal f max of the preset thresholdfrequency, transmitted by a PWM control signal generation unit (i.e. theIC Controller in the drawing), the other input receives the inductorvoltage frequency indication signal V_(ZCD), sent from the signalselection unit; the first logical NOR gate operator performs an NORoperation for f max and V_(ZCD), and the first logical NOR gate operatorgenerates a ZCD trigger signal flimit.

FIG. 8 is a schematic diagram illustrating timing of signals of afrequency limiting unit according to a second embodiment of the presentdisclosure. Similarly, f max is the pulse signal of the preset thresholdfrequency transmitted by the PWM control signal generation unit; V_(ZCD)is the inductor voltage frequency indication signal, the ZCD triggersignal flimit is generated after V_(ZCD) and f max are subjected to alogical NOR operation, in this case, a descending edge of flimit servesas a valid signal in the frequency limiting procedure. Optionally, apulse width of the PWM is calculated via loop control, depending on aninput voltage and an output load. The principle of FIG. 8 is the same asthe principle of FIG. 6 except that an ascending edge is adjusted to adescending edge, and details will not be descried herein again.

In summary, according to the frequency limiting unit provided in thisembodiment, the pulse signal of the preset threshold frequency of thePWM control signal generation unit and the inductor voltage frequencyindication signal transmitted by the signal selection unit are subjectedto a logical operation, and the result is transmitted to the PWM controlsignal generation unit as the ZCD trigger signal, the pulse signal ofpreset threshold frequency prevents the signal reversal of V_(ZCD)caused by changes of the inductor voltage from taking effect on the PWMcontroller, that is, as described above, the ascending edges of V_(ZCD)during the time period [t₃-t₄] and the time period [t₆-t₇] are invalid,during which the ZCD trigger signal flimit is not inverted, maintainingthe high voltage level. Further, the control circuit in this embodimentperforms the frequency limiting function based on an analog circuit,thus the signal processing procedure is simplified, the delay in theoutput control signal is reduced, and the requirement on performance ofthe processor is reduced, compared with the prior art where thefrequency limiting function is performed by a processor. The requirementof controlling of the entire PFC system is met due to improved accuracyof the signal processing in the PFC system.

Further, FIG. 9 and FIG. 10 illustrate a necessity of frequency limitingfor the ZCD trigger signal in this embodiment. FIG. 9 is a schematicdiagram illustrating timing of signals of a frequency limiting unitaccording to the present disclosure; FIG. 10 is a schematic diagram of arelationship between angle and operating frequency during a half sinecycle of mains frequency according to the present disclosure.

Specifically, FIG. 9 shows timing of signals of a PFC working under aDCMB operating condition. During the period from t₂ to t₄, there is anoscillation between the inductor and parasitic capacitors of theswitches, thus the voltage of the inductor and the voltage across theswitches oscillate. Therefore, according to the relationship between thevoltage of the inductor and the voltage VDS across the switches, usingthe ZCD trigger signal as a determining signal, the moment when VDSoscillates to zero (or the lowest voltage) can be identified and the PWMcontrol signal can be accordingly generated. With this method, it isensured that, when the voltage VDS is zero, i.e. at the time t₄, the PWMcontrol signal is outputted such that the switches Q1 and Q2 as shown inFIG. 1B and FIG. 1C are turned on. Therefore, for the PFC working inDCMB mode, the ZCD trigger signal can make sure that the power switch isturned on at zero voltage.

FIG. 10 is a diagram showing a relationship between angle and operatingfrequency during a half sine cycle of mains frequency of the inputvoltage Vac under a DCMB condition. The operating frequency is alsorelated to input voltage and output voltage. As shown in FIGS. 10, 264and 90 represent different effective value of input voltage. For the PFCworking in DCMB mode, a high operating frequency is required in avicinity of zero voltage crossing points, i.e. 0 degree and 180 degreesof the input Vac, in particular, the frequency will reach MHz for a highvoltage application. Meanwhile, since there is not much energytransferred in the vicinity of the zero voltage crossing points, thehigh frequency will lead to considerable switching loss. Therefore, itis necessary to limit the frequency of the ZCD trigger signal so as tolimit the high frequency switching loss at the zero voltage crossingpoints of the input Vac.

FIG. 11 is a schematic structural diagram of a control circuit accordingto a third embodiment of the present disclosure. The third embodiment ofthe control circuit as shown in FIG. 11 is a specific circuitimplementation based on the first embodiment. Voltages Va and Vb on twoauxiliary windings Laux1 and Laux2 are detected during the oscillationby coupling the auxiliary windings on the PFC inductor L_(PFC), and zerocrossing detection signal (Vsignal+ or Vsignal−) is generated via thecomparator. Since the detected wave on the auxiliary windings during thepositive and negative mains frequency half cycle are reverse, it isnecessary to select the Vsignal+ signal which is valid during thepositive half cycle and the Vsignal− signal which is valid during thenegative half cycle, and it is necessary to perform logical operationsfor Vsignal+, Vsignal− and the phase signal PD (the Vac phase detectionsignal) with the signal selection unit to generate a correct andeffective inductor voltage frequency indication signal V_(ZCD).

Specifically, as shown in FIG. 11, the signal detection unit includes: afirst winding Laux1, a second winding Laux2, a first resistor R1, asecond resistor R2, a third resistor R3, a fourth resistor R4, a firstcapacitor C1 and a second capacitor C2. The ZDC signal acquisition unitincludes a comparator. The first winding Laux1 and the second windingLaux2 are coupled with an inductor L_(FPC) at an input of the PFCcircuit and configured to obtain a voltage of an input AC of the PFCcircuit via a voltage of the inductor; a first end of the first windingLaux1 is connected to a first end of the first resistor R1, a second endof the first resistor R1 is connected to a first end of the secondresistor R2, a first end of the first capacitor C1 and a negative inputof the comparator; a second end of the first winding Laux1 is connectedto a first end of the second winding Laux2, a second end of the firstcapacitor C1, a first end of the second capacitor C2, a second end ofthe second resistor R2 and a first end of the fourth resistor R4; asecond end of the second winding Laux2 is connected to a first end ofthe third resistor R3; and a second end of the third resistor R3 isconnected to a second end of the second capacitor C2, a second end ofthe fourth resistor R4 and a positive input of the comparator; an outputof the comparator outputs the zero-crossing detection signal to thesignal selection unit.

The signal selection unit includes: a first logical AND gate operatorAND1, a first logical NAND gate operator NAND1, a second logical NANDgate operator NAND2, a second logical AND gate operator AND2, and asecond logical OR gate operator OR2. A first input of the first logicalAND gate operator AND1, and a first input and a second input of thesecond logical NAND gate operator NAND2 receive the zero-crossingdetection signal; a second input of the first logical AND gate operatorAND1, and a first input and a second input of the first logical NANDgate operator NAND1 receive a phase reference signal for the AC voltage;an output of the first logical NAND gate operator NAND1 and an output ofthe second logical NAND gate operator NAND2 are connected to a firstinput and a second input of the second logical AND gate operator AND2,respectively; an output of the first logical AND gate operator AND1 andan output of the second logical AND gate operator AND2 are connected toa first input and a second input of the second logical OR gate operatorOR2, respectively; an output of the second logical OR gate operator OR2outputs the inductor voltage frequency indication signal V_(ZCD) to thefrequency limiting unit. It should be noted that the first logical NANDgate operator and the second logical NAND gate operator may also be afirst logical NOT gate operator and a second logical NOT gate operator.

The frequency limiting unit includes the first logical OR gate operatorOR1. The two inputs of the first logical OR gate operator receive thepulse signal f max of the preset threshold frequency and the inductorvoltage frequency indication signal V_(ZCD), respectively; the firstlogical OR gate operator OR1 performs an OR operation for the pulsesignal of the preset threshold frequency and the inductor voltagefrequency indication signal; and the first logical OR gate operator OR1outputs the ZCD trigger signal to the PWM control signal generationunit. The PWM control signal generation unit is a digital processorDSP/MCU.

Further, FIG. 12A and FIG. 12B show a schematic diagram illustratingtiming of an inductor voltage detection signal and a zero-crossingdetection signal of a control circuit according to a third embodiment ofthe present disclosure. As shown in FIG. 12A and FIG. 12B, since thecomparator actually uses VCC as a single power supply, Va and Vb in theoperation timing diagram are operating voltages that can be identifiedby the comparator, and the minimum voltage is zero voltage. In a casewhere the positive input Vac is during the positive half cycle of themains frequency, when the inductor current IL decreases, Va isK*(Vout−Vac) (K is a proportional coefficient of the auxiliary winding)and Vb is zero voltage; when the inductor current is oscillated fromzero to negativity, Va will drop from K*(Vout−Vac) to zero voltage andVb will rise from zero voltage to K*Vac. In this process, thezero-crossing detection signal Vsignal+ is obtained by comparing thevoltage changes of Va and Vb. For the negative half cycle of the mainsfrequency, the obtaining of the zero-crossing detection signal isopposite to that during the positive half cycle of the mains frequency.

FIG. 13A and FIG. 13B show a schematic diagram illustrating timing of aninductor voltage frequency indication signal of a control circuitaccording to a third embodiment of the present disclosure. In thisembodiment, two intermediate signals are obtained according to thezero-crossing detection signal, which are respectively a positivezero-crossing detection signal Vsignal+ and a negative zero-crossingdetection signal Vsignal−. The positive zero-crossing detection signalVsignal+ is the zero-crossing detection signal, and the negativezero-crossing detection signal Vsignal− is an output signal after thezero-crossing detection signal is subjected to the NAND gate operation.When the phase signal PD is at high voltage level, the positivezero-crossing detection signal Vsignal+ and the PD are subjected to alogical AND operation to output Vsignal+; the signal Vsignal− and theflipped value of PD are subjected to an AND operation to output alow-level signal; finally, the Vsignal+ signal and the low level signalare subjected to a logical OR operation to output the V_(ZCD) signal,which is the signal Vsignal+. When the phase signal PD is at low voltagelevel, Vsignal+ and PD are subjected to a logical AND operation tooutput low voltage level signal; the signal Vsignal− and the flippedvalue of PD are subjected to an AND operation to output Vsignal−;finally, the Vsignal− signal and the low-level signal are subjected to alogical OR operation to output the V_(ZCD) signal, which is the signalVsignal−. Therefore, for the detected signals of different phases,corresponding signals may be individually extracted by the signalselection unit to obtain the inductor voltage frequency indicationsignal.

FIG. 14A and FIG. 14B show a schematic diagram illustrating timing of aZCD trigger signal of a control circuit according to a third embodimentof the present disclosure. As shown in FIG. 14, at the time t₀, both ofthe inductor voltage frequency indication signal V_(ZCD) and the pulsesignal of the preset threshold frequency f max are at high voltagelevels, V_(ZCD) and f max are subjected to an OR operation to produce anascending edge of flimit, the DSP identifies the ascending edge of theZCD trigger signal flimit, then CTR is cleared to restart counting; aperiod from t₀ to t₁ is dead time for the PWM, during which VDS of theswitch is oscillated to zero; during a period from t₁ to t₂, the PWMsignal is outputted to control turn-on time Ton of the switches; at thetime t₂, V_(ZCD) is changed from high voltage level to low voltagelevel, but f max maintains high voltage level, then flimit is notinverted, CTR continues counting; at the time t₃, the pulse signal f maxat the preset threshold frequency reaches the frequency-limiting time tochange to low voltage level, the ZCD trigger signal and flimit areinverted simultaneously, and CTR continues counting; at the time t₄,both V_(ZCD) and f max rises to high voltage levels, an ascending edgeof flimit is produced again, and CTR is cleared to restart counting;during a period from t₅ to t₆, the voltage level of V_(ZCD) changes, yetf max remains at high voltage level during this period, flimit remainsunchanged, and CTR continues counting; similarly, during a period fromt₇ to t₈, the level changing of V_(ZCD) is invalid; at the time t₈, fmax is inverted to low voltage level, however, yet V_(ZCD) is at highvoltage level, flimit remains unchanged, and CTR continues countinguntil the time t₉ when V_(ZCD) changes to low voltage level, and flimitis then inverted.

Optionally, the zero-crossing detection signal as shown in the aboveembodiment includes a phase signal of the voltage Vac. Correspondingly,the zero-crossing detection signal may also include: a voltage signalduring positive half cycle of and a voltage signal during negative halfcycle of the voltage. Adjustments need to be made to circuit structuresof the signal detection unit, the ZCD signal acquisition unit, and thesignal selection unit, respectively.

For instance, FIG. 15 is a schematic structural diagram of a signaldetection unit according to a first embodiment of the presentdisclosure, where an inductor voltage is detected using a singleauxiliary winding; FIG. 16 is a schematic structural diagram of a signaldetection unit according to a second embodiment of the presentdisclosure, where an inductor voltage is detected using a center-tappedauxiliary winding; FIG. 17 is a schematic structural diagram of a signaldetection unit according to a third embodiment of the presentdisclosure, where an inductor voltage is detected using two auxiliarywinding. The signal detection unit in embodiments of the presentdisclosure may be replaced with a circuit structure and animplementation as shown in FIG. 15 to FIG. 17 or as known to personsskilled in the art, and details will not be described herein again.

FIG. 18 is a schematic structural diagram of a ZCD signal acquisitionunit according to a first embodiment of the present disclosure,applicable in a case where input voltage only comprises positivehalf-wave or negative half-wave. A zero-crossing detection signal isdirectly outputted through a comparison of an inductor voltage detectionsignal VL obtained by the signal detection unit with a threshold Vref(Vref is a reference voltage value when the inductor current is zero) ofthe comparator; FIG. 19 is a schematic structural diagram of a ZCDsignal acquisition unit according to a second embodiment of the presentdisclosure; FIG. 20 is a schematic structural diagram of a ZCD signalacquisition unit according to a third embodiment of the presentdisclosure; and FIG. 21 is a schematic structural diagram of a ZCDsignal acquisition unit according to a fourth embodiment of the presentdisclosure. FIG. 19-FIG. 21 are applied in a case where the inputvoltage comprises both positive half-wave and negative half-wave. InFIG. 19, inductor voltage detection signals VL1 and VL2 obtained by thesignal detection unit are inputted to two comparators, where VL1 and VL2are comparison thresholds for each other, and two zero-crossingdetection signals Vsignal+ and Vsignal− are outputted to the signalselection unit finally; in FIG. 20, inductor voltage detection signalsVL1 and VL2 obtained by the signal detection unit are inputted to onecomparator, where VL1 and VL2 are comparison thresholds for each other,and only one zero-crossing detection signal Vsignal+ is outputted to thesignal selection unit finally; in FIG. 21, inductor voltage detectionsignals VL1 and VL2 obtained by the signal detection unit are inputtedto two comparators for respective comparisons with the threshold Vref ofthe comparators, and only two zero-crossing detection signals Vsignal+and Vsignal− are outputted to the signal selection unit finally. The ZCDsignal acquisition unit in embodiments of the present disclosure may bereplaced with a circuit structure and an implementation as shown in FIG.18 to FIG. 21 or as known to persons skilled in the art, and detailswill not be described herein again.

FIG. 22 is a schematic structural diagram of a signal selection unitaccording to a first embodiment of the present disclosure, which is usedto obtain positive and negative zero-crossing detection signals Vsignal+and Vsignal− when the input voltage comprises both positive half-waveand negative half-wave, where the signal selection unit may switch tothe inductor voltage signal of a phase by determining the correspondingphase of the Vac voltage. For instance, when PD is at high voltagelevel, the Vsignal+ signal is read, SW1 is turned off and SW2 is turnedon according to the PD signal, and the inductor voltage frequencyindication signal V_(ZCD) is the zero-crossing detection signalVsignal+; otherwise, when PD is at low voltage level, the inductorvoltage frequency indication signal V_(ZCD) signal is the Vsignal−.

FIG. 23 is a schematic structural diagram of a signal selection unitaccording to a second embodiment of the present disclosure, which usestwo MUXs (multiplexer) to select the zero-crossing detection signal,where the phase signal PD, controls the MUX chip selection enabling pinto determine whether or not to read the zero-crossing detection signalto obtain the V_(ZCD) signal; FIG. 24 is a schematic structural diagramof a signal selection unit according to a third embodiment of thepresent disclosure, which uses switches (such as an MOSFET or atransistor) to perform signal selection, where the phase signal PDdetermines, by controlling the switch drivers, whether or not to turn onthe corresponding switch to obtain the V_(ZCD) signal; FIG. 25 is aschematic structural diagram of a signal selection unit according to afourth embodiment of the present disclosure, which performs theselection of the zero-crossing detection signal with a combination oflogical operators. In this embodiment, the phase signal PD and thezero-crossing detection signal Vsignal+ are subjected to an ANDoperation, a flipped signal of the PD and the zero-crossing detectionsignal Vsignal− are subjected to an AND operation, then results of thetwo AND operations are subjected to a logical OR operation, and inductorvoltage frequency indication signals V_(ZCD) corresponding to differentphases may be obtained. When the phase signal PD is at high voltagelevel, the final result of logical operation is Vsignal+, which is alsothe final selected V_(ZCD) signal; otherwise, when the PD is at lowvoltage level, Vsignal− is the final selected V_(ZCD) signal. The signalselection unit in embodiments of the present disclosure may be replacedwith a circuit structure and an implementation as shown in FIG. 22 toFIG. 25 or as known to persons skilled in the art, and details will notbe described herein again.

Further, in the embodiments described above, FIG. 26A and FIG. 26B showa schematic diagram illustrating a principle of acquisition of a phasesignal by a signal selection unit according to a first embodiment of thepresent disclosure; and FIG. 27A and FIG. 27B show a schematic diagramillustrating a principle of acquisition of a phase signal by a signalselection unit according to a second embodiment of the presentdisclosure. In FIG. 26A and FIG. 26B, V_(L1) and V_(N1) of the inputvoltage Vac are respectively detected, V_(L1′) and V_(N1′) are obtainedthrough voltage divider resistors R1, R2, and R3, and the phase signalPD is finally obtained through a comparison by the comparator. Since thedetection circuit for the phase signal is applied in the Totem-polebridgeless PFC, voltage variations of V_(L1′) and V_(N1′) are affectedby the operating state of the bridgeless PFC. When the input Vac ispositive, V_(L1′) is a half sine wave and V_(N1′) is zero voltage; whenthe input Vac is negative, V_(L1′) is the sum of the negative half-cyclewaveform of the input sinusoidal AC voltage Vac and the value of the DCbus voltage Vbus, and V_(N1′) is the output Vbus voltage. In FIG. 27Aand FIG. 27B, Vac is detected via a differential amplifier, acorresponding proportion of Vac is obtained as Vac′, Vac′ is thendelivered to the comparator for a comparison with Vref (obtained byvoltage divider R6 and R7, and adjusted to the DC component of Vac′),and finally the phase signal PD is obtained. Since the detected value isthe difference between V_(L1) and V_(N1), the detected voltage hasalways been proportional to Vac regardless of the operating state of thebridgeless PFC.

FIG. 28 is a schematic flow chart of a control method according to afirst embodiment of the present disclosure. As shown in FIG. 28, thecontrol method according to the first embodiment of the presentdisclosure includes:

S101, detecting a voltage of an AC-side inductor;

S102, generating a zero-crossing detection signal according to thevoltage of the AC-side inductor;

S103, generating an inductor voltage frequency indication signalaccording to the zero-crossing detection signal;

S104, generating, according to a pulse signal of a preset thresholdfrequency, a ZCD trigger signal of a frequency no greater than thepreset threshold frequency; and

S105, generating a PWM control signal for an AC/DC converter accordingto the ZCD trigger signal.

The control method provided in the present disclosure is applied in thecontrol circuit as shown in FIG. 3, and their implementations andprinciples are the same, and details will not be described herein again.

In addition, an embodiment of the present disclosure further provides acomputer readable storage medium on which a computer program is stored,and the control method as shown in the above embodiments is implementedwhen the computer program is executed by a processor.

An embodiment of the present disclosure further provides a front-endprocessor, including:

a processor; and a memory for storing an executable instruction of theprocessor;

where the processor is configured to perform, upon execution of theexecutable instruction, the control method as shown in the aboveembodiments.

Finally, it should be noted that the foregoing embodiments are merelyintended for describing the technical solutions of the presentdisclosure rather than limiting the present disclosure. Although thepresent disclosure is described in detail with reference to theforegoing embodiments, persons of ordinary skill in the art shouldunderstand that they may still make modifications to the technicalsolutions described in the foregoing embodiments, or make equivalentreplacements to some or all technical features therein; however, thesemodifications or replacements do not make the essence of correspondingtechnical solutions depart from the scope of the technical solutions inthe embodiments of the present disclosure.

What is claimed is:
 1. A control circuit for outputting a pulse widthmodulation (PWM) control signal, comprising: a signal detection unit,coupled to an AC-side inductor of an AC/DC converter, which isconfigured to detect a voltage of the AC-side inductor and output aninductor voltage detection signal, wherein the inductor voltagedetection signal is an AC signal; a ZCD signal acquisition unit, coupledto the signal detection unit, which is configured to receive theinductor voltage detection signal, and generate a zero-crossingdetection signal of the voltage of the AC-side inductor; a signalselection unit, coupled to the ZCD signal acquisition unit, which isconfigured to receive the zero-crossing detection signal, and generatean inductor voltage frequency indication signal according to thezero-crossing detection signal; a frequency limiting unit, coupled tothe signal selection unit, which is configured to receive the inductorvoltage frequency indication signal and a pulse signal of a presetthreshold frequency, and generate a ZCD trigger signal of which thefrequency is no greater than the preset threshold frequency; and a PWMcontrol signal generation unit, coupled to the frequency limiting unit,which is configured to receive the ZCD trigger signal and generate a PWMcontrol signal for the AC/DC converter according to the ZCD triggersignal.
 2. The circuit according to claim 1, wherein the signaldetection unit, the ZCD signal acquisition unit, the signal selectionunit and the frequency limiting unit are constructed with analogcircuits.
 3. The circuit according to claim 1, wherein the frequencylimiting unit is configured such that: a first edge signal of the ZCDtrigger signal is generated when the pulse signal of the presetthreshold frequency and the inductor voltage frequency indication signalare both at high voltage levels; the ZCD trigger signal is not invertedwhen the pulse signal of the preset threshold frequency is at highvoltage level; when a descending edge of the pulse signal of the presetthreshold frequency arrives, if the inductor voltage frequencyindication signal is at low voltage level, then the ZCD trigger signalis inverted to output a second edge signal, if the inductor voltagefrequency indication signal is at high voltage level, then the ZCDtrigger signal is inverted to output a second edge signal when a nextdescending edge of the inductor voltage frequency indication signalarrives.
 4. The circuit according to claim 3, wherein the first edgesignal is at high voltage level and the second edge signal is at lowvoltage level.
 5. The circuit according to claim 4, wherein thefrequency limiting unit comprises a first logical OR gate operator; twoinputs of the first logical OR gate operator receive the pulse signal ofthe preset threshold frequency and the inductor voltage frequencyindication signal, respectively; the first logical OR gate operatorperforms an OR operation for the pulse signal of the preset thresholdfrequency and the inductor voltage frequency indication signal andgenerates the ZCD trigger signal.
 6. The circuit according to claim 3,wherein the first edge signal is at low voltage level and the secondedge signal is at high voltage level.
 7. The circuit according to claim6, wherein the frequency limiting unit comprises a first logical NORgate operator; two inputs of the first logical NOR gate operator receivethe pulse signal at the preset threshold frequency and the inductorvoltage frequency indication signal, respectively; the first logical NORgate operator performs a NOR operation for the pulse signal of thepreset threshold frequency and the inductor voltage frequency indicationsignal and generates the ZCD trigger signal.
 8. The circuit according toclaim 1, wherein the zero-crossing detection signal comprises a phasesignal of the AC-side inductor voltage.
 9. The circuit according toclaim 8, wherein the signal selection unit comprises: a first logicalAND gate operator, a first logical NAND gate or NOT gate operator, asecond logical NAND gate or NOT gate operator, a second logical AND gateoperator, and a second logical OR gate operator; a first input of thefirst logical AND gate operator, and a first input and a second input ofthe second logical NAND gate or NOT gate operator receive thezero-crossing detection signal; a second input of the first logical ANDgate operator, and a first input and a second input of the first logicalNAND gate or NOT gate operator receive a phase reference signal for theAC voltage; an output of the first logical NAND gate or NOT gateoperator and an output of the second logical NAND gate or NOT gateoperator are connected to a first input and a second input of the secondlogical AND gate operator, respectively; an output of the first logicalAND gate operator and an output of the second logical AND gate operatorare connected to a first input and a second input of the second logicalOR gate operator, respectively; an output of the second logical OR gateoperator outputs the inductor voltage frequency indication signal to thefrequency limiting unit.
 10. The circuit according to claim 9, whereinthe signal detection unit comprises: a first winding, a second winding,a first resistor, a second resistor, a third resistor, a fourthresistor, a first capacitor, a second capacitor, and the ZCD signalacquisition unit comprises a comparator; the first winding and thesecond winding are coupled to an AC-side inductor and configured toobtain an input AC voltage; a first end of the first winding isconnected to a first end of the first resistor, a second end of thefirst resistor is connected to a first end of the second resistor, afirst end of the first capacitor and a negative input of the comparator;a second end of the first winding is connected to a first end of thesecond winding, a second end of the first capacitor, a first end of thesecond capacitor, a second end of the second resistor and a first end ofthe fourth resistor; a second end of the second winding is connected toa first end of the third resistor; and a second end of the thirdresistor is connected to a second end of the second capacitor, a secondend of the fourth resistor and a positive input of the comparator; anoutput of the comparator outputs the zero-crossing detection signal tothe signal selection unit.
 11. The circuit according to claim 1, whereinthe zero-crossing detection signal comprises a positive half cycle of avoltage signal and a negative half cycle of the voltage signal of theinductor voltage.
 12. The circuit according to claim 1, wherein the PWMcontrol signal generation unit is a digital processor.
 13. A controlmethod for operating the control circuit of claim 1, comprising:detecting the voltage of an alternating current (AC)-side inductor;generating the zero-crossing detection signal according to the voltageof the AC-side inductor; generating the inductor voltage frequencyindication signal according to the zero-crossing detection signal;generating the ZCD trigger signal of a frequency no greater than thepreset threshold frequency, according to the inductor voltage frequencyindication signal and the pulse signal of the preset thresholdfrequency; and generating the PWM control signal for the AC/DC converteraccording to the ZCD trigger signal.